Coating compositions are know which are suitable for application to a substrate, for example, by spraying, dipping, electrodeposition or the like, which coating compositions are then cured by baking the coated substrate at an elevated temperature. Typically, such coating compositions comprise resinous materials or blends of resinous materials together with suitable crosslinking agent reactive with such resinous materials at elevated temperature.
In regard to electrodeposition of coatings, the process is well described in the art. Typically, an aqueous bath containing the coating composition is placed in contact with an electrically conductive anode and an electrically conductive cathode, and upon the passage of electric current (normally direct current) between the anode and the cathode while in contact with the bath containing the coating composition, an inherent film of the coating composition is deposited. Depending upon the nature of the coating composition, the coating may be deposited at the anode or at the cathode. The process parameters vary widely. The voltage applied may vary from as low as, for example, about one volt to as high as, for example, 500 volts or higher. Typically, however, the voltage used ranges from about 50 to about 400 volts.
A wide variety of electrodepositable resins are known to the skilled of the art. For example, a number of water-soluble, water-dispersable, or water-emulsifiable polycarboxylic acid resins can be electrodeposited. Such resins include, for example, reaction products or adducts of a drying oil or semi-drying oil fatty acid ester with a dicarboxylic acid or anhydride; interpolymers of a hydroxyalkyl ester of an unsaturated carboxylic acid, unsaturated carboxylic acid, and at least one other ethylenically unsaturated monomer; alkyd-amine vehicles, that is vehicles containing an alkyd resin and an amine-aldehyde resin; and mixted esters of resinous polyols. In U.S. Pat. No. 3,991,028 to Irwin et al, electrodepositable compositions are disclosed which comprise a water-dispersion of a hydrolyzed polyepoxide in combination with an interpolymer of a hydroxyalkyl ester, an unsaturated acid and at least one other monomer, and an amine-aldehyde resin. The use of a hydrolyzed polyepoxide is said to provide improved properties and to avoid agglomeration of the coating composition. In U. S. Pat. No. 4,026,855 to Parekh et al a coating composition is disclosed which is said to be adaptable for use in electrodeposition or as a water-based coating for application by spray or dip coating methods. The composition comprises an aqueous dispersion of (A) an ungelled modified crosslinking agent comprising certain aminoplast crosslinking agent that has been modified by reaction with a non-resinous hydroxyl-group containing carboxylic acid, and (B) a water-dispersable non-gelled polymeric material carrying a cationic charge and containing amino groups and at least one class of reactive groups selected fom carboxyl groups, alcoholic hydroxy groups and amide groups, and (C) an acid solubilizer. U.S. Pat. No. 4,033,917 to Sekmakas et al discloses certain copolymers of polyethylenically unsaturated epoxy-amine adducts and also stable aqueous dispersions containing same and also the electrodeposition of such aqueous dispersions at the cathode of a unidirectional electrical system. Specifically, amine functional polymers dispersable in water with the aid of a solublizing acid are said to be provided by copolymerizing (A) certain ethylenically unsaturated hydroxy functional amine adduct free of epoxy groups, and (B) copolymerizable monoethylenically unsaturated monomers, a portion of which is amine-functional. The copolymer is said to be dispersable in water at certain pH and to be electrodepositable at the cathode, optionally together with an aminoplast curing agent to provide coatings which can be cured usually by exposure to elevated temperature. U.S. Pat. No. 3,471,388 to Koral is directed to a cathodic electrocoating composition which incorporates an aminoplast crosslinker with any of several disclosed resins. One disclosed resin is an aminated polymer containing hydroxy groups. Numerous suitable hydroxy-containing aminated polymers are suggested which have capability to crosslink with an aminoplast crosslinking agent. One such suggested polymer is the reaction product of a poly-functional amine with a poly-functional epoxy compound. The polyhydroxy polymers are said to be disperable in water upon addition of suitable acid such as acetic acid. Additional related teaching directed to coating compositions suitable for use in electrocoating processes is provided in U.S. Pat. No. 4,159,233 to Ting et al; U.S. Pat. No. 4,057,523 to Blank; U.S. Pat. No. 4,182,831 to Hicks; U.S. Pat. No. 4,192,932 to Dickie, which patent is assigned to the assignee of the present application; U.S. Pat. No. 4,192,929 to Bloomfield, which patent is assigned to the assignee of the present application; U.S. Pat. No. 4,202,746 to Lee et al; and U.S. Pat. No. 4,072,536 to Otsuki et al.
It is a primary objective of the present invention to provide a crosslinkable polymeric resin and a crosslinkable coating composition comprising same. In this regard, it is one particular object of the invention to provide a crosslinkable coating composition adapted for use in primer compositions such as a primer composition for an automotive vehicle body, to effectively retard corrosion of the underlying substrate. It is particularly an objective of the invention to provide such corrosion protection without the use of chromate pigments.
One particular objective of the invention is to provide a crosslinkable coating composition comprising an aqueous dispersion of such crosslinkable resin for use in the electrodeposition of coatings onto electrically conductive substrates. In this regard, it is a particular objective to provide coating compositions adapted for use in cathodic electrocoating processes. Additional objects and aspects of the invention will be apparent from the following description thereof.